JPH03205566A - Current intensity transformer - Google Patents

Abstract

PURPOSE: To obtain a current intensity transformer which can measure a direct current upon which a strong high-frequency vibrating component is superimposed or a low-frequency alternating current by providing a measurement circuit which generates a signal which is the function of a magnetic field in the void of a magnetic circuit and another signal which is the function of a winding current. CONSTITUTION: A current Ip to be measured flows through a conductor 1 and a magnetic circuit 2 having a void 3 surrounds the conductor 1. A measuring winding 4 is connected to a measuring resistor R through a switch 6. A Hall battery 5 is placed in the void 3. An energizing current (i) is supplied to the battery 5 from a circuit incorporating a Zener element Z and a transistor T and the potential at a terminal 8 is controlled by means of an operational amplifier 11. A terminal 9 is maintained at a reference potential and a measured voltage for ground proportional to the magnetic field H in the void 3 is obtained at a terminal 10. Then the measured voltage is inputted to an operational amplifier 13 and the level of the output USD from a terminal 15 is adjusted by means of a variable resistor. The output US indicates the actual magnetic flux in the void 3. The measured voltage appears at a terminal M through the resistor R. At the time of calibrating the voltage US against UR, a direct current or sine wave alternating current is used as a reference main current and, when the sine wave current is used, the winding 4 is disconnected by opening the switch 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a current intensity transformer comprising a magnetic circuit having at least one air gap, the air gap being provided with a magnetic field detector; The magnetic circuit relates to a current intensity transformer for measuring a variable current, which is arranged in magnetic coupling with the current conductor to be measured and is magnetically associated with at least one measuring winding.

[Conventional technology]

This type of device is known, for example, from European Patent No. 0
No. 194 225.

Such known devices operate according to the theory of compensation of the magnetic field generated by the current to be measured on the one hand and by the measuring current passed through the measuring winding on the other hand.

[Invention or problem to be solved]

In certain applications, such as the measurement of pulsed currents or periodic currents with strong asymmetrical waveforms or switch-on currents of alternating current networks, conventional current transformers become saturated and are therefore unusable. Furthermore, it is desirable to be able to take into account the determination of direct current or low-frequency alternating current on which strong high-frequency vibration components are superimposed, using a relatively simple, inexpensive, and compact device.

The present invention aims to provide a device that solves this need.

[Means to solve the problem]

For this reason, the device according to the invention provides, on the one hand, a 141st constant signal (US
), on the other hand, it has an electrical measuring circuit arranged to produce a second measuring signal (UR) which is the number of currents in said measuring winding.

Preferably, the magnetic field detector is a Hall effect device, and the measuring circuit is arranged to generate, as a first measuring signal, a first measuring voltage (US) adjustably proportional to the magnetic field in the air gap, and a second all constant. The signal is the voltage (UR) appearing at the terminals of a measuring resistor connected in series with said measuring winding.

Preferably, the measuring circuit is arranged to add the first and second measured voltages.

The measuring circuit is such that a sinusoidal reference current flowing in said conductor for the current to be measured is generated at the terminals of said measuring resistor by means of an ideal current strength converter without air gaps when the measuring winding is interrupted. More preferably, it is arranged and adjusted to generate a measured voltage equal to the theoretical voltage that would exist.

In a preferred embodiment, the Hall effect device is connected to the energizing current generator by an input power supply terminal and an output power terminal, the output power terminal of the Hall effect device being connected to the output terminal of a power amplifier having two input terminals. Preferably, one of the terminals is connected to a measuring reference potential, such as ground, and the other of these inputs is connected to one of the measuring terminals of the Hall effect device. In this case, one measuring terminal of the Hall-effect device is held at a reference potential, and the measuring voltage obtained by the Hall-effect device appears at the other constant terminal ρ with respect to said reference potential.

The device according to the invention comprises an adjustable gain amplifier, one input of which is applied with a flj+ constant voltage generated by a Hall effect device, one output of which is connected to one terminal of said measuring resistor, said resistor The other terminal of forms the output terminal of the measuring circuit. The measurement resistor can also be connected to the output terminal of a Hall effect device that generates the measurement signal, and the Hall effect device is connected to a current generator that supplies an adjustable energizing current through the power supply terminal. Forced.

The device according to the invention may comprise two or more air gaps, each air gap having a magnetic field detector, each detector generating a signal that is a function of the magnetic field in the corresponding air gap, and the measurement circuit detecting these detectors. and a second ifllj constant signal which is a function of the current in the measuring winding.

The device according to the invention comprises a safety circuit arranged to detect an increase in the measured voltage generated by the Hall effect device above at least one threshold, and is configured to generate a fault signal when such an increase occurs. More preferred.

Other features, advantages and features of the invention will become apparent from the following description of an exemplary embodiment, which is illustrated in the accompanying drawings.

〔Example〕

In the diagram of Figure 1, the main current to be measured! , is conductor 1
The conductor 1 is laterally surrounded by a magnetic circuit 2 having an air gap 3. This magnetic circuit may be of the type, for example, of an annular core made of a highly permeable material or laminated metal plates forming a laminated structure similar to the transformer core.

A measuring winding 4 is arranged on this magnetic circuit and is connected to the measuring resistor R through a connecting device, schematically indicated by a switch 6. The Hall battery 5 is placed within the gap 3 so as to be affected by the magnetic field appearing in the gap 3. The Hall battery 5 is shown separately in the diagram of FIG. 1 with its connections. The energizing current l is, for example, the first
Transistor T1 resistor r connected to power supply terminal 7
1, r2 and a Zener diode Z through a current generator. As shown in FIG.
The first itFl constant terminal 9 of the Hall battery, connected to do. Therefore, at the second measuring terminal 10 of the Hall cell there appears a measuring voltage relative to ground that is proportional to the magnetic field H occurring in the air gap 3.

The output terminal 10 is connected to a first input terminal 12 of an operational amplifier 13, whose second input terminal 14 is connected to the midpoint of a voltage divider connected between ground and the output terminal 15 of this operational amplifier 13. There is. In the case of a voltage divider, it has a fixed resistor r3 and a variable resistor r, and the variable resistor r is the output terminal 15.
It is possible to control the level of the measured voltage U8 present at , and to adjust the proportionality constant between this voltage and the magnetic field H.

When the current IP to be measured contains, for example, a DC component and a variable component, the direct component induces a back electromotive force in the winding 4. This winding is connected to a resistor "rrR, with a corresponding amperage AT s, the main amperage AT s, i.e. in this case, and during the magnetic field H P゜, where L is the width of the air gap, ATP-H- L+AT
The function holds true. The voltage U5 indicates the magnitude of a certain H-L of the main current l,S, which fraction indicates the magnetization of the magnetic circuit, ie actually the magnetic flux in the air gap. This is because the extremely high magnetic permeability of the iron parts of the circuit negates the magnetomotive force required for the magnetic flux circulating in the rest of the circuit. With respect to the voltage UR at the terminals of the resistor R, the measurement of the fraction of the main current is compensated by the secondary ampere-turns resulting from the surge of magnetic flux.

To calibrate the voltage U, with respect to the voltage U, a reference mains current is used, which can be a direct R current or a sinusoidal current. Winding 4 is calibrated by a stop string current.
is interrupted by opening the switch 6, and the current measurement is made only by the M+ constant of the magnetic field in the air gap. The voltage U8 is regulated by setting the gain of the multiplier 13 by the resistor r, and the vibration of U8 is equal to the voltage U that the ideal current strength without air gaps would be generated by the transformer.
It is equal to the theoretical value of the amplitude of R, that is, in this case, if N8 is the number of turns of winding 4, then U - R-1, /N8S. When voltages UR and U8 are added, it becomes direct (AI). 3
A value of the total current strength including 2 minutes can be obtained. In the diagram of FIG. 1, the total measured voltage appears at terminal M and resistor R
is connected between terminal 15 and M.

According to an embodiment (not shown) of the invention, the measuring resistance R
is connected to the lfi-connected Hall battery, i.e. to its terminal 10, and is powered by a current generator which generates an adjustable energizing current making it possible to adjust the output voltage of the Hall battery.

It is also possible to ground one terminal of the resistor R and add the voltage UR to the output voltage of the Hall battery, and the output voltage can be calculated according to a known method. It can be amplified or unamplified by a suitable resistor connected to the input of the Ii amplifier. However, if the resistor R is connected in series with the measuring voltage US, The advantage of not introducing distortion to the measurement signal UR is obtained by limiting the width.

The device according to the invention is suitable for the precise measurement of pulsed currents or short-circuit currents of large amplitude, or for large mains currents with a relatively small continuous component, as well as for short-duration measurements such as switch-on charging of alternating current networks. This is particularly advantageous in the case of alternating mains current measurements with a certain amount of direct current.

The diagram of FIG. 1 further shows a safety circuit device, designated 16, which is adapted to detect an increase of the M1 constant voltage obtained by the Hall battery, in the direction of one pole or the other, above a threshold value. It is composed of Therefore, terminal 15
are connected to the respective inputs "1" and "+" of the two comparators 17 and 18, and the corresponding inputs of the opposite signs of these comparators are connected to the terminals of the series connection of the two Zener diodes, and their common connection The points are connected through resistors to the positive and negative voltage supply terminals of the circuit, respectively. A potentiometer 19 is connected in parallel with these Zener diodes, the slider of which is connected to the input 20 of the summation amplifier 11 through a resistor r4, and a resistor ``5'' connected between this input and ground. This potentiometer can offset the offset voltage of U8 when there is no main current,
The offset voltage is obtained by adding the offset voltages of the battery 5 and the amplifiers 11 and 13.

The output terminals of the converters 17, 18, consisting of transistors with open collectors, are connected together and through a resistor to the positive terminal of the voltage supply.

Each comparator is connected in such a way that it conducts when the applied measuring voltage exceeds a threshold defined by the voltage of the corresponding Zener diode in the direction of the polarity of this voltage. An output signal such as a negative error (E) then appears in the illustrated circuit and also produces a no longer linear effect, for example within the saturation of the magnetic circuit or the Hall cell.

In some applications, it may be advantageous to divide the magnetic circuit into two shunts, so as to obtain a circuit in which the main resistor can be inserted into the open circuit. In this case, the magnetic circuit is e.g.
It has two air gaps, each with a hole zh, and the separately adjustable constant voltage of these cells is applied to the measuring circuit. The measuring windings can be placed in the two branches of the magnetic circuit and can be hinged like a chip-on ammeter.

The number of gaps and corresponding Hall cells is not limited to two, but is preferably two or more if the current to be measured is extremely large.

In the case of a device with several batteries, the addition of the different battery voltages can be done, for example, by connecting the terminal 1o of the first battery to the input of the power supply circuit of the later battery, i.e. to the terminal corresponding to terminal 20. do. The voltage appearing at an output such as output terminal 10 of each cell then forms the base potential of the subsequent current, and the measured voltage of every current appears at the output of the last cell.

On the other hand, if the measured voltage is relatively small, the DC
It is preferable to use a main conductor made from several windings to increase the accuracy.

〔Effect of the invention〕

The invention provides an electric current arranged to generate, on the one hand, a first measurement signal that is a function of the magnetic field in the air gap of the magnetic circuit and, on the other hand, a second measurement signal that is a function of the current in the measurement winding. By having a measuring circuit, it is possible to measure, with a relatively simple, inexpensive and compact device, the direct current component of the current that can or should be measured separately, and to measure the direct current component of the current that can be or is to be measured separately, as well as of pulsed currents or periodic currents with strong asymmetrical waveforms. Or the switch-on current of an alternating current network can be measured.

[Brief explanation of drawings]

The drawing shows a current transformer arrangement according to the invention with a measuring circuit. 1... Conductor, 2... Magnetic circuit, 3... Air gap, 4...
... Measuring winding, 5... Hall battery, 6... Switch, 7... First power supply terminal, 8... Second power supply terminal, 9... First measurement terminal, 10... ...Second measurement terminal,
1 1 -. ．． Operational amplifier, 12... first input terminal,
13... Arithmetic amplifier, 14... Second input terminal, 15
...Output terminal, 16...Safety circuit device, 17, 18
···comparator.

Claims (1)

[Claims] 1. A current intensity transformer comprising a magnetic circuit having at least one air gap, the air gap being provided with a magnetic field detector, and the magnetic circuit is connected to a current conductor to be measured and a magnetic field detector. In a current strength transformer for measuring a variable current, which is arranged to be combinable and magnetically combined with at least one measuring winding, on the one hand, the current strength transformer is a function of the magnetic field in the air gap of said magnetic circuit; 1 measurement signal (U_S),
On the other hand, a second
Current strength transformer, characterized in that it has an electrical measuring circuit arranged to generate a measuring signal (U_R). 2. The magnetic field detection device is a Hall effect device, and the measuring circuit is arranged to generate a first measuring signal (U_S) adjustably proportional to the magnetic field in the air gap as the first measuring signal; 2. Device according to claim 1, characterized in that the measuring signal is a voltage (U_R) appearing at the terminals of a measuring resistor connected in series with the measuring winding. 3. The device according to claim 1, characterized in that the measuring circuit is arranged to add the first and second measured voltages. 4. The measuring circuit is constructed based on the theory that a sinusoidal reference current passing through the current conductor to be measured would be generated at the terminals of the resistor by an ideal current strength without a gap in the cut-off state of the measuring winding. 4. Device according to claim 3, characterized in that it is arranged and adjusted to generate a measuring voltage equal to the voltage. 5. The power supply terminal of the Hall effect device is connected to the output terminal of an operational amplifier having first and second inputs, the first input being connected to a measuring reference potential such as ground, and the second input being connected to a measuring reference potential, such as ground. connected to a first measuring terminal of a Hall effect device, wherein said first measuring terminal is maintained at a reference potential and a measuring voltage generated by the Hall effect device appears at said second measuring terminal with respect to said reference potential. 2. A Hall effect device having an input power supply terminal and an output power supply terminal connected to energize the current generator, and wherein the magnetic field sensing device having the first and second measuring devices is a Hall effect device. or any one of claims 2 to 4. 6. has an adjustable gain amplifier, one input of which is applied the output signal generated by the Hall effect device, one output of which is connected to one terminal of the measuring device, and the other terminal of this resistor is 6. A device according to any one of claims 3 or 4, 3 and 5, 4 and 5, forming an output terminal of a measuring circuit. 7. A measuring resistor is connected to the output terminal of the Hall effect device,
or any of claims 3 and 5 or 4 and 5, characterized in that the Hall effect device is energized through a power supply terminal of a current generator providing an adjustable energization current. The device according to item 1. 8. The magnetic circuit has two or more air gaps each equipped with a magnetic field detector, each detector generating a signal that is a function of the magnetic field in the corresponding air gap, and the measuring circuit being supplied by these detectors. 8. The device according to claim 1, wherein the device is arranged to add a second measurement signal which is also a function of the current in the measurement winding. 9. A safety circuit according to any one of claims 2 to 8, comprising a safety circuit arranged to detect an increase in the measured voltage generated by the Hall effect device above at least one threshold value and to generate a false signal when said increase occurs. The equipment described in section.